“EARLY MICROBIAL PROGRAMMING begins in utero and is substantially modulated by mode of birth, perinatal antibiotics and breastfeeding … this stepwise microbial colonization process … might have a long-lasting influence on the risk of not only gastrointestinal disease, but also allergic, autoimmune and metabolic disease, in later life.”
http://www.nature.com/nrgastro/journal/v9/n10/abs/nrgastro.2012.144.html